With most silver halide color photographic materials, three photographic silver halide emulsion layers spectrally sensitized to blue, green and red light are coated on a support. For example, with silver halide photographic materials for color negatives, a blue-sensitive silver halide emulsion layer on which incident light first falls, a green-sensitive silver halide emulsion layer, and a red-sensitive silver halide emulsion layer are coated on a support in that order. Usually, a bleachable yellow filter is disposed between the blue- and green-sensitive emulsion layers so as to absorb any of the blue light that has passed through the blue-sensitive layer. Other intermediate layers having various functions are placed between each emulsion layer, and a protective layer is provided as the outermost layer. It is known to arrange the respective light-sensitive emulsion layers in different orders than shown above. It is also known to use a light-sensitive silver halide emulsion layer unit that consists of two layers that are sensitive to substantially the same wavelength region but which have different sensitivities. These silver halide color photographic materials use aromatic primary amine compounds as typical color developing agents, which develop exposed silver halide grains so that the oxidation product of the developing agent reacts with a dye forming coupler to form the desired dye image. In this method of color development, different couplers are used to form cyan, magenta and yellow dye images: cyan couplers are those based on phenols and naphthols; magenta couplers are based 5-pyrazolone, pyrazolinobenzimidazole, pyrazolotriazole, indazolone and cyanoacetyl compounds; and yellow couplers are based on acylacetamides. These dye forming couplers are incorporated in either the appropriate light-sensitive silver halide emulsion layers or a developing solution. The photographic material contemplated by the present invention may be of either type, but in a preferred embodiment, the couplers are rendered non-diffusible by incorporation in silver halide emulsion layers.
Recently, in the photographic industry, there has been an increasing demand for silver halide color photographic materials that have high sensitivity and which are capable of producing an image of high quality. One reason for this demand is the increasing desire to take pictures under less favorable conditions such as insufficient light (e.g. shooting indoors) and use of telephoto lens or zoom lens which are subject to accidental movement because of their heavy weight. Secondly, the consumer's preference for small formats has obviously given incentives to the development of silver halide color photographic materials that not only have high density but also produce images of good quality in terms of sharpness, granularity and interimage effect.
However, higher sensitivity and better image are two requirements that are difficult to satisfy at the same time. First, with respect to the usual layer arrangement wherein red-, green- and blue-sensitive silver halide emulsion layers are coated in sequence on a support, with the red-sensitive layer lying closest to the support, it has been proposed that higher sensitivity can be obtained by modifying part or all of the light-sensitive silver halide emulsion layers in such a manner that a certain emulsion layer is divided into two layers having sensitivity to substantially the same color of light and placed one immediately above the other, one being a layer of higher sensitivity and the other of lower sensitivity, and each containing non-diffusible couplers that will develop substantially the same color.
Two problems are noticeable in this layer arrangement: firstly, the light-sensitive silver halide emulsion layer positioned closer to the support receives an insufficient amount of incident light for exposure since the greater part of light is absorbed by the other light-sensitive emulsion layers which are farther from the support; secondly, the developing solution takes a longer time to reach the emulsion layers positioned closer to the support. Because of this insufficient exposure and retarded development, the green- and red-sensitive silver halide emulsion layers which are closer to the support than the blue-sensitive layer are not completely adapted to the achievement of higher sensitivity.
Layer arrangements that are modifications of the above described usual arrangement are also known. For example, U.S. Pat. No. 3,663,228 discloses the following two-unit structure, wherein:
(a) red-, green- and blue-sensitive silver halide emulsion layers of lower sensitivity are coated on a support, with the red-sensitive layer closest to the support, so as to make an RGB lower-sensitivity layer unit (said RGB denote red, green and blue, respectively; hereinafter the same.);
(b) on said RGB lower-sensitivity layer unit, red-, green- and blue-sensitive silver halide emulsion layers of higher sensitivity are coated, with the red-sensitive layer closest to the support, so as to make an RGB higher-sensitivity layer unit.
According to U.S. Pat. No. 3,663,228, the RGB higher-sensitivity layer unit is isolated from the RGB lower-sensitivity layer unit by a neutral density (ND) filter. The use of this ND filter clearly shows that the achievement of higher sensitivity is not at all contemplated by the invention of said U.S. patent. In addition, the performance of the claimed two-unit structure falls short of satisfying the requirements for high quality.
A green-sensitive silver halide emulsion layer has significant effects on spectral luminous efficiency, and U.S. Pat. No. 3,658,536 discloses a technique for counteracting the insufficiency of exposure given to this green-sensitive layer by providing it in a position farther from the support. This alteration of layer arrangement, however, is not sufficient to provide better granularity.
The followings techniques have been proposed as modified layer arrangements capable of achieving higher sensitivity.
(A) Unexamined Published Japanese Patent Application No. 49027/1976 discloses a structure wherein:
(a) red- and green-sensitive silver halide emulsion layers of lower sensitivity are coated on a support, with the red-sensitive layer closer to the support, so as to make an RG lower-sensitivity layer unit;
(b) on said RG lower-sensitivity layer unit, red- and green-sensitive silver halide emulsion layers of higher sensitivity are coated, with the red-sensitive layer closer to the support, so as to make an RG higher-sensitivity layer unit;
(c) on said RG higher-sensitivity layer unit, two blue-sensitive silver halide emulsion layers, one having the higher sensitivity and the other having the lower sensitivity, are coated as in the usual layer arrangement to provide a B unit.
(B) Unexamined Published Japanese Patent Application No. 97424/1978 discloses a silver halide color photographic material having the same layer arrangement as in (A) except that each of the red- and blue-sensitive silver halide emulsion layers in the RG lower-sensitivity layer unit is divided into two layers, one having a medium sensitivity and the other having a low sensitivity.
(C) Japanese Patent Application No. 52115/1983 filed by the applicant of subject application proposes a structure wherein an RGB higher-sensitivity layer unit and an RGB lower-sensitivity layer unit are coated in sequence on a support.
The silver halide color photographic materials with the layer arrangements (A), (B) and (C) are common in that at least a red-sensitive silver halide emulsion layer having high sensitivity is disposed between a green-sensitive silver halide emulsion layer of high sensitivity and a green-sensitive layer having a lower sensitivity than the first green-sensitive emulsion layer. These arrangements are effective in achieving the objectives of obtaining a higher sensitivity and better image quality but are still insufficient to satisfy the recent requirements for providing images of super-high quality.